The present invention relates generally to all-wheel drive motor vehicles, and more particularly, to a power take-off unit providing full-time four-wheel drive to the front and rear drivelines.
In recent years, there has been a significant increase in the demand for motor vehicles equipped with a powertrain capable of providing drive torque to all four wheels. Traditional four-wheel drive vehicles are equipped with a longitudinally-extending engine and transmission that deliver power to the input of a transfer case which, in turn, distributes the power to the front and rear drivelines. As is known, some transfer cases are equipped with a transfer clutch for automatically transferring power to the front driveline during lost traction situations to establish an xe2x80x9con-demandxe2x80x9d four-wheel drive mode. Other transfer cases are equipped with an interaxle differential which functions to transmit power to both drivelines during normal conditions at a predetermined torque distribution ratio so as to establish a full-time four-wheel drive mode. Such four-wheel drive vehicles are typically based on a rear wheel drive arrangement and, as such, are generally limited to SUV""s and trucks.
To provide drive torque to the rear wheels in front wheel drive vehicles, a power take-off unit (PTU) is driven by the output of a front-wheel drive transaxle and supplies power to the rear driveline. Typically, such an all-wheel drive arrangement delivers torque automatically (i.e., on-demand) through a transfer clutch to the rear driveline upon lost traction at the front wheels. Recently, a great deal of development effort has been directed at packaging the PTU and the remaining rear driveline components within the underbody of conventional front-wheel drive vehicles. Thus, a need exists to develop new AWD powertrain arrangements which are compact in size, can be packaged into existing front-wheel drive vehicles, and provide features (i.e., full-time AWD, automatic torque biasing) that enhance performance.
It is therefore an object of the present invention to provide an all-wheel drive system for a motor vehicle equipped with a transversely mounted engine and transmission assembly.
As a related object, the all-wheel drive system includes a power take-off unit having an interaxle differential which drives a first power path connected to the front wheels and a second power path connected to the rear wheels. The first power path includes a planetary final drive unit which drives a double planetary front differential unit that is interconnected to a pair of front axleshafts. The second power path includes a helical gearset and a bevel gearset which deliver power to a rear propshaft.
As further object, the PTU of the present invention may include an electronically-controlled biasing clutch assembly operable to control interaxle speed differentiation and torque-biasing.
These and other objects, advantages and features of the present invention will be apparent from studying the following detailed description and the drawings which, while disclosing the invention in the best mode currently known for carrying out the invention, are not intended to be limiting but rather exemplary of one application currently contemplated.